c++: libcpp: Support raw strings with newlines in directives [PR55971]

It's not currently possible to use a C++11 raw string containing a newline as
part of the definition of a macro, or in any other preprocessing directive,
such as:

 #define X R"(two
lines)"

 #error R"(this error has
two lines)"

Add support for that by relaxing the conditions under which
_cpp_get_fresh_line() refuses to get a new line. For the case of lexing a raw
string, it's OK to do so as long as there is another line within the current
buffer. The code in cpp_get_fresh_line() was refactored into a new function
get_fresh_line_impl(), so that the new logic is applied only when processing a
raw string and not any other times.

libcpp/ChangeLog:

	PR preprocessor/55971
	* lex.cc (get_fresh_line_impl): New function refactoring the code
	from...
	(_cpp_get_fresh_line): ...here.
	(lex_raw_string): Use the new version of get_fresh_line_impl() to
	support raw strings containing new lines when processing a directive.

gcc/testsuite/ChangeLog:

	PR preprocessor/55971
	* c-c++-common/raw-string-directive-1.c: New test.
	* c-c++-common/raw-string-directive-2.c: New test.

gcc/c-family/ChangeLog:

	PR preprocessor/55971
	* c-ppoutput.cc (adjust_for_newlines): Update comment.

1 files changed, 32 insertions, 9 deletions

diff --git a/libcpp/lex.cc b/libcpp/lex.cc
index cc12a52d..b110792 100644
--- a/libcpp/lex.cc
+++ b/libcpp/lex.cc
@@ -1076,6 +1076,9 @@ _cpp_clean_line (cpp_reader *pfile)
   buffer->next_line = s + 1;
 }
 
+template <bool lexing_raw_string>
+static bool get_fresh_line_impl (cpp_reader *pfile);
+
 /* Return true if the trigraph indicated by NOTE should be warned
    about in a comment.  */
 static bool
@@ -2695,9 +2698,8 @@ lex_raw_string (cpp_reader *pfile, cpp_token *token, const uchar *base)
 	{
 	  pos--;
 	  pfile->buffer->cur = pos;
-	  if (pfile->state.in_directive
-	      || (pfile->state.parsing_args
-		  && pfile->buffer->next_line >= pfile->buffer->rlimit))
+	  if ((pfile->state.in_directive || pfile->state.parsing_args)
+	      && pfile->buffer->next_line >= pfile->buffer->rlimit)
 	    {
 	      cpp_error_with_line (pfile, CPP_DL_ERROR, token->src_loc, 0,
 				   "unterminated raw string");
@@ -2712,7 +2714,7 @@ lex_raw_string (cpp_reader *pfile, cpp_token *token, const uchar *base)
 	    CPP_INCREMENT_LINE (pfile, 0);
 	  pfile->buffer->need_line = true;
 
-	  if (!_cpp_get_fresh_line (pfile))
+	  if (!get_fresh_line_impl<true> (pfile))
 	    {
 	      /* We ran out of file and failed to get a line.  */
 	      location_t src_loc = token->src_loc;
@@ -2724,8 +2726,15 @@ lex_raw_string (cpp_reader *pfile, cpp_token *token, const uchar *base)
 		_cpp_release_buff (pfile, accum.first);
 	      cpp_error_with_line (pfile, CPP_DL_ERROR, src_loc, 0,
 				   "unterminated raw string");
-	      /* Now pop the buffer that _cpp_get_fresh_line did not.  */
+
+	      /* Now pop the buffer that get_fresh_line_impl() did not.  Popping
+		 is not safe if processing a directive, however this cannot
+		 happen as we already checked above that a line would be
+		 available, and get_fresh_line_impl() can't fail in this
+		 case.  */
+	      gcc_assert (!pfile->state.in_directive);
 	      _cpp_pop_buffer (pfile);
+
 	      return;
 	    }
 
@@ -3659,11 +3668,14 @@ _cpp_lex_token (cpp_reader *pfile)
 }
 
 /* Returns true if a fresh line has been loaded.  */
-bool
-_cpp_get_fresh_line (cpp_reader *pfile)
+template <bool lexing_raw_string>
+static bool
+get_fresh_line_impl (cpp_reader *pfile)
 {
-  /* We can't get a new line until we leave the current directive.  */
-  if (pfile->state.in_directive)
+  /* We can't get a new line until we leave the current directive, unless we
+     are lexing a raw string, in which case it will be OK as long as we don't
+     pop the current buffer.  */
+  if (!lexing_raw_string && pfile->state.in_directive)
     return false;
 
   for (;;)
@@ -3679,6 +3691,10 @@ _cpp_get_fresh_line (cpp_reader *pfile)
 	  return true;
 	}
 
+      /* We can't change buffers until we leave the current directive.  */
+      if (lexing_raw_string && pfile->state.in_directive)
+	return false;
+
       /* First, get out of parsing arguments state.  */
       if (pfile->state.parsing_args)
 	return false;
@@ -3706,6 +3722,13 @@ _cpp_get_fresh_line (cpp_reader *pfile)
     }
 }
 
+bool
+_cpp_get_fresh_line (cpp_reader *pfile)
+{
+  return get_fresh_line_impl<false> (pfile);
+}
+
+
 #define IF_NEXT_IS(CHAR, THEN_TYPE, ELSE_TYPE)		\
   do							\
     {							\